true-color detection

[adamyg]

Consider true-color detection option, set rgb then inquire result.

Querying The Terminal

In an interactive program that can read terminal responses, a more reliable method is available, that is transparent to sudo & ssh.

Simply try sending a truecolor value to the terminal, followed by a query to ask what color it currently has. If the response indicates the same color as was just set, then truecolor is supported.

If the response indicates an 8-bit color, or does not indicate a color, or if no response is forthcoming within a few centiseconds, then assume that truecolor is not supported.

$ ( printf '\e[48:2:1:2:3m\eP$qm\e\\' ; xxd -g1 )

^[P1$r48:2:1:2:3m^[\
00000000: 1b 50 31 24 72 34 38 3a 32 3a 31 3a 32 3a 33 6d  .P1$r48:2:1:2:3m

Here we set the background color to RGB(1,2,3) - an unlikely default choice - and request the value that we just set. The response comes back that the request was understood (1), and that the color is indeed 48:2:1:2:3. This tells us also that the terminal supports the colon delimiter. If instead, the terminal did not support truecolor we might see a response like

^[P1$r40m^[\
00000000: 1b 50 31 24 72 34 30 6d 1b 5c 0a              .P1$r40m.\.

This terminal replied that the color is 40 - it has not accepted our request to set 48:2:1:2:3.

^[P0$r^[\
00000000: 1b 50 30 24 72 1b 5c 0a                      .P0$r.\.

This terminal did not even understand the DECRQSS request - its response was CSI+0$r. This does not indicate whether it set the color, but since it doesn't understand how to reply to our request it is unlikely to support truecolor either.